Method for producing a dentist tool

ABSTRACT

Method for producing a dentist tool formed by an overlay to be used by a dentist in removing tooth structure, said method comprising the steps of: acquiring three-dimensional data relating to a shape of a tooth and at least a part of a neighbouring tooth;
         processing said three-dimensional data with a computer so as to determine an overlay fitting said tooth and fitting at least said part of said neighbouring tooth;   further processing said three-dimensional data with said computer so as to determine a predetermined part of tooth structure to be removed from said tooth so as to prepare said tooth for further treatment;   determining at least two guiding edges of which a first and a second guiding edge are spaced apart from each other by a distance d of at least 0.5 mm, said guiding edges being configured so as to enable said dentist cutting tool to be guided by simultaneously contacting said first and said second guiding edge in such a manner as to enable a guided removal of at least partially said predetermined part of tooth structure;   producing said determined overlay having said determined guiding edges.

The present invention concerns a method for producing a dentist toolformed by an overlay to be used by a dentist in removing toothstructure, said method comprising the steps of:

acquiring three-dimensional data relating to a shape of at least onepredetermined tooth and at least a part of a neighbouring tooth of saidpredetermined tooth;

processing said three-dimensional data with a computer so as todetermine an overlay fitting said tooth and fitting at least said partof said neighbouring tooth;

determining guiding means within said overlay, suitable for guiding adentist cutting tool;

producing said determined overlay having said determined guiding means.

The present invention further concerns a dentist tool obtained by theapplication of the described method.

When a patient needs a crown, bridge, onlay, inlay, veneer, or otherrestoring and/or aesthetic tooth treatment, conventionally, during aninitial office visit, the dentist identifies the needs of the patientand determines an appropriate treatment. During subsequent visits, incase the tooth comprises damaged and/or infected tooth structure, thedentist removes this tooth structure and reconstructs the tooth as muchas possible using conventional techniques. Thereafter, the dentistperforms the final preparation of the tooth for further treatment byremoving tooth material, which is to be interpreted as original toothstructure and reconstructed tooth structure, with a dental cutting toolsuch as a high-speed drill. Relying upon eyesight and expertise, thedentist uses the drill to shape the tooth in a form that is suitable forfurther treatment, in particular a form onto which a crown, bridge,onlay, inlay, veneer or other tooth restoring part can be mounted. Then,the dentist takes an impression of the dental arch in which the preparedtooth is located, and sends the impression to the dental laboratory tohave the dental technician make the restoration part. Using theimpression of the prepared tooth, the dental technician produces arestoration part that matches the colour, geometrical and materialspecifications, and sends it to the dentist. At the patient's finalvisit, the dentist adjusts the restoration part as necessary beforefitting it in place.

Such a dentist tool is disclosed in EP1547544. The known dentist tooldecreases the impact of the experience and expertise of the dentist ontothe treatment, and it is used by a dentist in boring an artificial toothroot cavity. In EP1547544, guiding means, formed by a cylindrical hole,for guiding a drill in a straight-forward way, is provided. In such amanner an artificial tooth root cavity can be bored with greaterprecision even by a less experienced dentist. Moreover a suitable rootcavity position can be calculated based on the information processed bythe computer, so as to form in the most optimal way a cavity in the jawbone.

A drawback of the known dentist tool is that it can only be used by adentist in boring holes into the jaw bone. This dentist tool is notsuitable to be used by a dentist in preparing a tooth for furthertreatment.

It is an object of the present invention to provide method for producinga dentist tool that is suitable for being used by a dentist in preparinga tooth for further treatment.

To this end, a dentist tool according to the present invention ischaracterized in that said method comprises the further steps of:

before determining said guiding means, determining a predetermined partof tooth structure to be removed from said tooth so as to prepare saidtooth for further treatment;

determining at least two guiding edges of which a first and a secondguiding edge are spaced apart from each other by a distance of at least0.5 mm, said guiding edges being part of said guiding means (7), saidguiding edges being configured so as to enable said dentist cutting toolto be guided by simultaneously contacting said first and said secondguiding edge in such a manner as to enable a guided removal of at leastpartially said predetermined part of tooth structure.

The determination of a predetermined part of tooth structure to beremoved results in that this does not any more depend on the skills ofthe dentist. Depending on the individual dental situation of a patient,the computer is programmed to determine an optimal way for shaping thetooth into a shape that is suitable for further treatment. Determiningand producing guiding edges into an overlay, which guiding edges aresuitable for simultaneously contacting the dentist cutting tool, allowsthe cutting tool to be guided along a well determined path in an atleast partially predetermined way. The overlay, having the guidingedges, accurately indicates onto the tooth the part to be removed fromthe tooth as determined by the computer. Moreover the tool according tothe invention is provided to assist the dentist in removing toothstructure as the tool allows a dentist to remove at least part of apredetermined part of tooth structure.

It is to be noted that the term fitting is not to be interpreted in thenarrow sense that the overlay should closely surround the teeth. Itmoreover should be interpreted as that an overlay should surround theteeth so as to be adequately in contact with the teeth and so that, onceapplied, it will not be released even if certain pressure, due to anormal use of the overlay, is applied.

In a preferred embodiment of the invention, said first and said secondguiding edge are designed for simultaneously contacting said dentistcutting tool at contacting points being longitudinally distanced fromeach other by said distance, said guiding edges thereby defining aguiding surface along which said dentist cutting tool is to be guided.

By simultaneously contacting two guiding edges with a cutting tool atcontacting points being longitudinally distanced from each other, thecutting tool can be guided at least partially in a predetermined way.Preferably the cutting tool moves along the two guiding edges andthereby defines a guiding surface. This surface comprises the twoguiding edges, and a cutting tool can be guided along this surface. Thisallows an accurate guiding in two dimensions.

Preferably, in determining said guiding means, a guiding groove isdetermined, which defines a path extending in a surface of said overlayand suitable for guiding said dentist cutting tool along said path insuch a manner as to enable a guided removal of at least partially saidpredetermined part of tooth structure.

The two guiding edges, being distanced from each other, can be locatedone on the one side and the other on the other side of the path therebydefining the path between the two guiding edges. To this purpose, thedistance between the two guiding edges should be substantially equal toa diameter of the cutting tool. Using the dentist cutting tool bysimultaneously contacting the two guiding edges and following the pathallows a guidance of the cutting tool at least in two dimensions.Considering a longitudinal cutting tool, the surface defined by the twoguiding edges in this configuration will be substantially perpendicularto the direction of the cutting tool in use.

The two guiding edges, being distanced from each other, can also be bothlocated on one side of the path. At least a third guiding edge will thendefine the other side of the path. Considering a longitudinal cuttingtool in this configuration, the surface defined by the two guiding edgeswill be substantially parallel to the direction of the cutting tool inuse. The third guiding edge in this configuration will provide a furtherguidance to the cutting tool thereby increasing the accuracy of theprocess of removal of tooth structure. Using the dentist tool bysimultaneously contacting the two guiding edges and following the pathin this configuration allows a guidance of the cutting tool in twodimensions and a guidance of inclination of the cutting tool.

Preferably, the method comprises the further steps of:

determining a tooth restoration part having an inner shape so as to fita remaining part of tooth structure of said tooth, and having an outershape so as to fit together with remaining neighbouring teeth;

producing said tooth restoration part.

An advantage of the method according to the invention is that the shapeof the remaining part of tooth structure of the prepared tooth is knownin advance due to the guided removal of tooth structure. This improvesfurther treatment, such as preparing a temporary or final inlay, onlay,bridge, crown or veneer in advance based on the three-dimensional data.This results in that less office visits are required, as the dentist canboth prepare the tooth and mount the tooth restoration part onto theprepared tooth in one single visit. This way of working does not onlysave time and thus costs, also the inconvenience for the patient isstrongly decreased. Furthermore the chances that a prepared tooth getscontaminated, and the resulting complications, are reduced to a minimum.

Preferably, said predetermined part is determined by:

firstly determining a tooth restoration part having an outer shape so asto fit together with remaining neighbouring teeth, and having an innershape compatible with said outer shape;

secondly determining a shape of remaining tooth structure so that saidtooth restoration part having said inner shape fits said shape ofremaining tooth structure;

thirdly determining said predetermined part as being the part of toothstructure to be removed so as to have said shape of remaining toothstructure left.

Starting with determining a tooth restoration part instead of, asconventionally, preparing the tooth, has an advantage. A toothrestoration part can be determined having an outer shape so as tooptimally fit together with remaining neighbouring teeth. Procedures fordetermination of such an outer shape are known to the person skilled inthe art. An inner shape is then determined, which inner shape iscompatible with said outer shape. Criteria for being compatible dependon the material that is to be used and mainly concern strengthparameters, production parameters and parameters relating to themounting of the restoration part onto the tooth and/or teeth. Preferablythe inner shape is determined in such a manner that a minimum amount ofmaterial is required to produce the tooth restoration part. This at itsturn results in that the remaining tooth structure, required to fit tothis inner shape, is as large as possible, namely, the more material ofa restored tooth is tooth restoration material, the less material ofthat restored tooth is tooth structure. Then the predetermined part canbe determined as being the part of tooth structure to be removed so asto have said shape of remaining tooth structure left. Thus firstdetermining the tooth restoration part, results in that a minimum oftooth structure is to be removed from the tooth and maximum conservationof the original tooth structure. As it is best to maintain as much ofthe original tooth structure, this is an advantage.

In a further step, the determined tooth restoration part having thedetermined outer and inner shape, can be produced. This results in thatless office visits are required, as the dentist can prepare the toothand mount the tooth restoration part onto the prepared tooth in onesingle visit, having the advantageous as described above.

Preferably said removal of tooth structure is to be performed in aplurality of stages in which said guiding means is provided to guidesaid cutting tool in a first stage of said plurality of stages, and atleast one further guiding means is provided to guide said cutting toolin at least one further stage, the method further comprising the stepsof:

determining said at least one further guiding means (7) each comprisingat least two further guiding edges of which a further first and afurther second guiding edge are spaced apart from each other by adistance of at least 0.5 mm, said further first and said further secondguiding edges being provided for simultaneously contacting said dentistcutting tool thereby guiding said dentist cutting tool in such a manneras to enable a guided removal of at least partially said predeterminedpart of tooth structure;

producing at least one further overlay each having one of said at leastone further guiding means.

Producing a plurality of overlays instead of just one overlay provides afurther flexibility in the method for producing the dentist tool.Different overlays can be provided for guiding a dentist cutting toolalong different sides of the tooth to be prepared, so that for example acircumferential path can be defined by using multiple overlays eachdefining a different segment of the circumferential path. Multipleoverlays furthermore allow to use different dental cutting tools, whichis necessary in some cases. Different overlays can be provided forpreparing a tooth in multiple stages, in which for example a first stageis provided to smoothen the upper part of the tooth, a second and athird stage are provided to cut away the longitudinal and transversalsides of the tooth, and a fourth and fifth stage are provided to roundoff the edges between the longitudinal and transversal sides each at adifferent side of the tooth. Preparing a tooth in stages allows eachoverlay to be designed having guiding edges which are particularlydetermined for guiding the cutting tool in a particular waycharacterised by the particular stage.

The invention will now be described in more details with respect to thedrawings illustrating some preferred embodiments of the invention. Inthe drawings:

FIG. 1 shows a top view of an overlay with a guiding groove according tothe invention;

FIG. 2 shows a side view of an overlay with a guiding groove placed ontoa patient's teeth.

FIG. 3 shows a cross section of part of an overlay with guiding meansaccording to one embodiment of the invention and a cutting tool;

FIG. 4 shows a cross section of part of an overlay with guiding meansaccording to another embodiment of the invention and a cutting tool;

FIG. 5 shows a cross section of part of an overlay with guiding meansaccording to the invention and a cutting tool;

FIG. 6 shows a cross section of part of an overlay with guiding meansaccording to a further embodiment of the invention and a cutting tool;

FIG. 7 shows a set of overlays to be used by a dentist in preparing atooth for mounting a crown or bridge.

FIG. 8 shows a cross-section of the overlay shown in FIG. 7 a.

In the drawings a same reference number has been allocated to a same oranalogous element.

The terms “lower”, “upper” etc. and derived directional terms such as“horizontal” and “vertical” are based on a normal configuration of anoverlay as shown in the drawings, wherein the overlay fits onto teethwith their root extending vertically downward. The term dentist in thistext is not to be interpreted restrictive and can also be read as dentaltechnician, dental assistant, dental auxiliary, dental therapist, dentaldesigner etc.

The invention provides a method for producing a dentist tool formed byan overlay 1 to be used by a dentist in removing tooth structure.Furthermore, the invention provides an overlay 1 obtainable by thismethod. FIG. 1 and 2 show such an overlay 1 arranged onto the teeth 2 ofa patient. Preferably, the invention provides a method for producing thedentist tool and a tooth restoration part in such a manner that thetooth restoration part will fit the tooth that is prepared using thedentist tool.

The dentist tool according to the invention is preferably used by adentist in preparing a tooth for a restoration such as placing inlaysand onlays, crowns, bridges, and veneers. Such restoration requires arestoration part to be produced in order to fit the tooth after thelatter has been prepared. Using the dentist tool according to theinvention results in that the shape of the prepared tooth, whichconventionally is only known after preparation, is determined inadvance. Based on this knowledge, a restoration part can be produced inadvance so that this restoration part is available to the dentist evenbefore he or she starts preparing the tooth, and can be mounted directlyafter preparation of the tooth. This results in that the patient suffersless inconvenience, in particular that the number of visits to thedentist are reduced. Furthermore the chances that a prepared tooth getscontaminated, and the resulting complications, are reduced to a minimum.

Preferably, preparing a tooth for further treatment is performed onto asubstantially healthy tooth. When a tooth is damaged or infected, thedamaged and/or infected parts of the tooth will have to be removedfirst, and the tooth will have to be reconstructed before preparing thetooth for further treatment. This minimizes the chance that an infectiondevelops underneath a tooth restoration part. This also maximizes thelifetime of the tooth restoration part as the basis for the toothrestoration part, namely the tooth, does not contain damaged parts anymore.

Several methods are known for acquiring three-dimensional data from apatient's dentition. Such data can be retrieved by processingphotographs taken from the patient's dentition. Another method is makinga physical impression of the dentition and then scanning this impressionwith a CAD/CAM 3D scanning device. For what concerns the presentinvention, any appropriate method for acquiring three-dimensional datacan be used.

After acquiring the three-dimensional data of the tooth, this data getsprocessed by a computer so as to determine an overlay 1 fitting theteeth 2 of the patient. To this end, the inner shape of the overlaypreferably corresponds to the outer shape of the tooth to be preparedand to the outer shape of at least part of a neighbouring tooth. Overlayshould fit the teeth in such a manner that once the overlay is placedonto the teeth, it will only come off by applying a sufficiently highforce to the overlay. During preparation of the tooth, small forces maybe applied to the overlay, which preferably should not modify theposition of the overlay on the teeth. Preferably, the overlay 1 extendsover the teeth 2 so as to also cover part of the gingiva 3 for stabilitypurpose and protection purpose. As the dentist will use the overlay 1for removing tooth material, it is advantageous that the overlay 1 islocated onto the tooth in a stable way. As an example, an overlay 1closely fitting the tooth, two neighbouring teeth, and part of thegingiva 3, ensures that a dentist can arrange and maintain the overlayin a stable position during removal of tooth structure. When the overlay1 covers a part of the gingiva 3, at least this part of the gingiva 3will be protected during the process of removing tooth structure.

It is to be noted that an overlay 1 according to the invention can covermultiple teeth at once and can be provided to be used by a dentist inpreparing a plurality of teeth using one single overlay 1. This can beadvantageous in the process of preparing teeth for placing veneers. Suchan overlay comprises guiding means, as will be explained further, foreach tooth that needs to be prepared.

The determined overlay 1 has a thickness 4 that mainly depends on therequired strength thereof, and thus also the material it will be madeof. An overlay 1 according to the invention can have a constant overallthickness 4. A substantially constant overall thickness is preferred foran overlay to be used by a dentist in preparing a tooth or teeth forplacing veneers. An overlay to be used for preparing a tooth for placinga bridge or a crown preferably comprises an upper, guiding part 5, and alower, supporting part 6. The supporting part 6 of the overlay 1 willensure that the overlay 1 can be arranged in a stable way onto the teeth2, whereas the guiding part 5 of the overlay 1 will guide the dentistcutting tool and preferably will also determine the maximal penetrationdept of the cutting tool in the tooth. To this end, the thickness of theguiding part 5 of the overlay 1 will preferably be determined case bycase together with the determination of the guiding means 7, as will beexplained further. The thickness 4 of the supporting part 6 of theoverlay 1 can be more freely chosen depending on the preferences of thedentist and/or the programmation of the computer.

After acquiring the three-dimensional data, this data gets alsoprocessed by a computer so as to determine a predetermined part of toothstructure to be removed from the tooth by the dentist. The predeterminedpart will be determined in view of the further treatment. If aparticular shape of the prepared tooth is required for allowing furthertreatment, the predetermined part will be chosen so that afterpreparation of the tooth, this particular shape will remain.

Determining the predetermined part depends on many parameters and willdiffer from case to case. Parameters are the location of the tooth inthe mouth of the patient, amount and location of the damaged toothstructure, distance of the tooth to neighbouring teeth, etc. In apreferred embodiment, the computer will also take into account thedifferent parts of the tooth such as the enamel, dentin, pulp, cementum,etc. in determining the predetermined part.

According to the invention, the computer is programmed to determine thepredetermined part of tooth structure to be removed without assistanceof a dentist except for what concerns the input of the initial data ofthe tooth. However also according to the invention, the computer can beprogrammed to determine the predetermined part in cooperation with adentist, where for example the dentist decides on some parameters. Thiscooperation can be established by visualizing data relating to the toothonto a computer display and allowing the dentist at least to enter oneparameter relating to the preparation of the tooth. Preferably a previewof the tooth is visualized onto the computer display together with apreview of a simulation of the prepared tooth, so as to allow a dentistto see the impact of chosen parameters onto the prepared tooth. Thelatter feature provides a larger degree of freedom to the dentist andallows a less experienced dentist to consult a more experienced dentistabout a case, based on the data in the computer. In this manner, themethod for producing a dentist tool according to the invention allows aless experienced dentist to decide on a further treatment and prepare atooth for further treatment with a same quality as if he or she was anexperienced dentist.

In another embodiment, the computer is programmed to determine thepredetermined part of tooth structure to be removed in several phases.At the end of each phase, the computer proposes a simulated solution tothe dentist and requests for approval or correction of the proposedsolution.

Preferably the predetermined part will be determined in several steps.In a first step, the outer shape of the tooth restoring part is to bedetermined so that the tooth restoring part fits with the remainingteeth and fits into the dental arch of the patient. A bite lift or othercorrective amendment can be directly integrated into the design of theouter shape. Then, based on this determined outer shape, an inner shapegets determined that is compatible with the outer shape. In such amanner, a tooth restoration part can be determined having an optimalouter shape, and an optimal construction in the sense that it is strongenough and a minimum of material is needed. In a following step, theshape of remaining tooth structure is to be determined so that the innershape of the tooth restoring part fits the remaining tooth structureafter removal of tooth structure. In a final step, the predeterminedpart of tooth structure is determined as the part of tooth structure tobe removed to have the shape of remaining tooth structure left. This wayof working allows determining the outer shape of the tooth restoringpart using best fit programs. Conventionally, the dentist will notfollow the steps in the succession as mentioned above. The dentist willwork the other way around, as the dentist will need to know the shape ofthe prepared tooth to determine the inner shape of the restoration part,after which the dentist will determine an appropriate outer shape.Firstly determining the tooth restoration part, according to a preferredembodiment of the invention, results in that a minimum of toothstructure is to be removed from the tooth and a maximum conservation ofthe original tooth structure can be obtained.

Once the predetermined part has been determined, guiding means can bedetermined. The purpose of the guiding means is to guide a dentistcutting tool, i.e. a drill, so that the cutting tool removes at least apart of the predetermined part. To this end, it will be understood thatin some cases, the dimensions of the dentist cutting tool, such as thelength, diameter, cross-sectional form, etc. will be determining forwhich movement is to be made with the cutting tool to remove a certainpart of tooth structure. It will also be understood that in many cases,it will not be sufficient to make one single movement for removing allthe predetermined part. Via computer calculation and/or simulation, oneor more movements can be determined for removing the predetermined partof tooth structure. It is to be understood that a movement in thiscontext does not only relates to a two-dimensional position, but relatesto the movement of the cutting tool in all its aspects such ashorizontal movement, vertical movement and tilt movement.

The guiding means according to the invention comprise at least twoguiding edges 11, 12 (FIG. 3-6). Two of these guiding edges 11, 12 arespaced apart from each other with a distance d of at least 0.5 mm. Theguiding edges 11, 12 are provided to simultaneously contact the cuttingtool 10 thereby guiding the cutting tool 10 at least partially into apredetermined movement. It is to be understood in this context that asurface having a length and having a width which are at least 0.5 mm canbe considered as the said at least two guiding edges 11, 12. Namely, thetwo outer edges of the surface are provided to simultaneously contactthe cutting tool 10, and are spaced apart with a distance d of at least0.5 mm.

Preferably the two guiding edges 11, 12 are spaced apart from each otherwith a distance d of at least 1 mm, more preferably of at least 2 mm andmost preferably of at least 3 mm. Increasing the distance d between thetwo edges 11, 12 will increase the guiding quality as it will be mucheasier for a dentist to control the cutting tool 10 onto larger guidingmeans.

The guiding edges 11, 12 are provided in such a manner as to besimultaneously contacted by the cutting tool at two contacting points.As illustrated in FIG. 3, preferably these contacting points 11, 12,considered on the cutting tool 10, are longitudinally spaced apart bythe distance d. When the cutting tool 10 is arranged substantiallyperpendicular to the guiding edges, the distance between the contactingpoints will be substantially the same as the distance d between theguiding edges. FIG. 3 illustrates a cutting tool 10 lying simultaneouslyagainst the two guiding edges 11, 12. The guiding edges 11, 12 in thisconfiguration define a surface along which the cutting tool 10 can beguided.

However the guiding edges 11, 12 can also simultaneously contact thecutting tool 10 at two contacting points being located each at one sideof the cutting tool 10, as illustrated in FIG. 4. In this configuration,the guiding edges 11, 12 define a guiding groove in which the cuttingtool 10 can be guided. The guiding groove 7 is preferably determined soas to define a path laying in the upper surface of the overlay 1. Thegroove 7 is provided for guiding a dentist cutting tool along this path,and to this end, the groove 7 extends through the overlay so as to forma communication between the inside of the overlay and the outerenvironment. When more than one path is to be followed for removing thepredetermined part, multiple guiding grooves 7 will have to bedetermined.

A combination of these two mentioned configurations is illustrated inFIG. 5. In this figure, a first and second guiding edge 11, 12, beingthe two guiding edges that are spaced apart, can be seen on the lefthand side, which edges define a guiding surface. A third guiding edge 13can be seen on the right hand side, which edge defines, together withthe first and second guiding edge 11, 12, a path. This configurationtherefore allows a cutting tool to be guided into both a horizontalmovement and a tilt.

As can be seen in FIG. 5, the cutting tool 10 preferably comprises acollar 14 mounted onto the cutting tool 10. Preferably at least one ofthe guiding edges 11, 12, 13 is provided to guide the collar 14 of thecutting tool 10 thereby guiding the cutting tool 10 into a predeterminedvertical position or height or depth. As can be seen in the FIG. 5, theguiding groove 7 defining a horizontal path, furthermore defines apredetermined height 8 for each horizontal location of the cutting tool,so as to guide the cutting tool 10 along a horizontal path and in apredetermined tilt, and also guiding the cutting tool in the verticalway.

FIG. 6 illustrates a variant on the embodiment shown in FIG. 3, andshows the guiding edges 11, 12, which are provided to simultaneouslycontact the cutting tool at two contacting points being longitudinallydistanced from each other. In this embodiment, tooth structure can beremoved that is located in between the two guiding edges 11, 12. Inparticular in preparing a tooth for placing veneers, this embodimentwill be used.

For mounting a crown or a bridge, the tooth is to be shaped into atruncated pyramid having rounded edges. To this end the outer and upperpart of the tooth are to be removed. This removal of tooth structure canbe guided by the dentist tool according to the invention.

Preferably the removal of tooth structure for preparing a tooth formounting a crown or a bridge is performed in several stages shown inFIG. 7. In a first stage, shown in FIG. 7a and FIG. 8, the upper part ofthe tooth gets smoothened. This can be done using an overlay havingguiding edges 11, 12 as illustrated in FIG. 6. However in practice, itis preferred that the upper part gets shaped into a V-form. To this end,the upper part preferably gets smoothened using two guiding means asillustrated in FIG. 3, which guiding means are located on both sides ofthe tooth in such a manner that said guiding means are provided guidesaid cutting tool to cut said upper part into a V-shape.

In a second and a third stage, shown in FIGS. 7 b and 7 c, thelongitudinal and transversal sides of the tooth get cut, so as to obtaina truncated pyramid form. The cutting of these sides can be guided byoverlays having guiding means as illustrated in FIG. 3, 4 or preferablyFIG. 5. Preferably one overlay comprises two such guiding means eachdefining a path extending in the surface of the overlay, the pathsextending parallel to each other, each on one side of the tooth.

In a fourth and fifth stage, shown in FIGS. 7 d and 7 e, the edges ofthe pyramid get rounded. Rounding these edges can be guided by anoverlay as shown in FIG. 1 and 2. Such an overlay comprises a pathextending in the surface of the overlay and defining a segment of acircle. Each side of the path is defined by a guiding surface having atleast two guiding edges, as illustrated in FIG. 3. The height of theguiding part 5 of the overlay 1 is defined so as to guide the cuttingtool 10 in a predetermined vertical position.

In this succession of stages, the first stage could be executed as thelast stage instead of as the first. However tests have shown thatstarting with smoothening the upper part of the tooth is advantageous inthe process of preparing the tooth.

Once the overlay 1 and the guiding means are determined, the determinedoverlay 1 having the determined guiding means can be produced. This canbe done by any known means such as a CAD/CAM system, rapid prototypingor 3D printing. When multiple guiding means have been determined,multiple overlays 1 can be produced each comprising one or severalguiding means.

The overlay 1 has, as already mentioned above, a lower, supporting part6 and an upper, guiding part 5. As can be seen in the figures, theguiding part 5 has a certain thickness 8, which defines the height 8 ofthe path and enables the cutting tool to be guided in the vertical way.Preferably the supporting part 6 and/or guiding part 5 comprises avertical opening 9 from the side to the guiding groove 7, provided toserve as an entrance into the guiding groove 7 for a dental cuttingtool. In particular when a cutting tool has a tip portion that has adiameter that is larger than the diameter of the main portion of thecutting tool, for example a high-speed drill with a tip in the form of aball, this opening is advantageous. Entering such a cutting tool intothe guiding groove 7 via the upper part of the overlay would at leastpartially widen the guiding groove 7 thereby at least partially takingaway its possibility to firmly guide the cutting tool along thepredetermined path. Furthermore a side entrance 9 is preferred over anentrance via the upper part as it will be easier to enter the cuttingtool in a controlled manner into the guiding groove 7.

When a guiding groove 7 is determined to form a circular path in thehorizontal plane, it will be preferred to split up this path intoseveral segments, and produce multiple overlays 1 each having a guidinggroove 7 corresponding to one segment of this path. This will result ina set of overlays 1 which can be used by a dentist one after the otherto remove tooth structure following this circular path. Each overlay 1of the set of overlays 1 will guide the cutting tool along a particularside of the tooth.

In the embodiment where the predetermined part is not determined basedon the shape of the tooth restoration part, the latter can be determinedbased on the data in the computer. Outer shape of the tooth restorationpart can be determined in several ways, all known to the person skilledin the art. A bite lift or other corrective amendment can be directlyintegrated into the design of the outer shape. A first possibility is toshape the tooth restoration part so that it resembles the outer shape ofthe original tooth. A second possibility is to shape the toothrestoration part so that it fits with neighbouring teeth. A thirdpossibility is a combination of the first and second, and modifies theshape of the original tooth to better fit with the neighbouring teeth.Inner shape of the tooth restoration part will be determined based onthe simulation of the preparation of the tooth. As the tooth will beprepared in a guided manner, it is known in advance what the shape willbe of the prepared tooth. The inner shape of the tooth restoration partwill be chosen so that it fits the shape of the prepared tooth.

Preferably the method according to the invention further comprises thestep of producing a tooth restoration part.

Similar to the determination of the predetermined part, a toothrestoration part can be determined by a computer without any interactionof a dentist. However it will be preferred that the computer determinesthe tooth restoration part in cooperation with a dentist, for example ina way as described above. The computer can, in this process ofdetermining a tooth restoration part, perform predetermined clinicalchecks and alert the dentist in case the tooth restoration part does notmeet the standard norms. This will enable a dentist to design a toothrestoration part in a fast and reliable manner.

The production of the tooth restoration part can be done by any meansknown to the skilled person such as a CAD/CAM system.

1. Method for producing a dentist tool formed by an overlay (1) to beused by a dentist in removing tooth structure, said method comprisingthe steps of: acquiring three-dimensional data relating to a shape of atleast one predetermined tooth and at least a part of a neighbouringtooth of said predetermined tooth; processing said three-dimensionaldata with a computer so as to determine an overlay (1) fitting saidtooth and fitting at least said part of said neighbouring tooth;determining guiding means (7) within said overlay (1), suitable forguiding a dentist cutting tool; producing said determined overlay (1)having said determined guiding means (7), characterized in that saidmethod comprises the further steps of: before determining said guidingmeans (7), determining a predetermined part of tooth structure to beremoved from said tooth so as to prepare said tooth for furthertreatment; determining at least two guiding edges of which a first and asecond guiding edge are spaced apart from each other by a distance d ofat least 0.5 mm, said guiding edges being part of said guiding means(7), said guiding edges being configured so as to enable said dentistcutting tool to be guided by simultaneously contacting said first andsaid second guiding edge in such a manner as to enable a guided removalof at least partially said predetermined part of tooth structure. 2.Method according to claim 1, characterised in that said first and saidsecond guiding edge are designed for simultaneously contacting saiddentist cutting tool at contacting points being longitudinally distancedfrom each other by said distance d, said guiding edges thereby defininga guiding surface along which said dentist cutting tool is to be guided.3. Method according to claim 1, characterised in that in determiningsaid guiding means, a guiding groove is determined, which defines a pathextending in a surface of said overlay and suitable for guiding saiddentist cutting tool along said path in such a manner as to enable aguided removal of at least partially said predetermined part of toothstructure.
 4. Method according to claim 1, characterised in that themethod comprises the further steps of: determining a tooth restorationpart having an inner shape so as to fit a remaining part of toothstructure after removal of tooth structure of said tooth, and having anouter shape so as to fit together with remaining neighbouring teeth;producing said tooth restoration part.
 5. Method according to claim 1,characterised in that said predetermined part is determined by: firstlydetermining a tooth restoration part having an outer shape so as to fittogether with remaining neighbouring teeth, and having an inner shapecompatible with said outer shape; secondly determining a shape ofremaining tooth structure so that said tooth restoration part havingsaid inner shape fits said shape of remaining tooth structure; thirdlydetermining said predetermined part as being the part of tooth structureto be removed so as to have said shape of remaining tooth structureleft.
 6. Method according to claim 5, characterised in that said methodfurther comprises the step of producing said tooth restoration part. 7.Method according to claim 1, characterised in that said dental cuttingtool comprises a cutting portion and a collar, one of said at least twoguiding edges being designed to guide said collar along so as to enablesaid dentist cutting tool to be guided into a longitudinal position. 8.Method according to claim 1 characterised in that said removal of toothstructure is to be performed in a plurality of stages in which saidguiding means is provided to guide said cutting tool in a first stage ofsaid plurality of stages, and at least one further guiding means isprovided to guide said cutting tool in at least one further stage, themethod further comprising the steps of: determining said at least onefurther guiding means (7) each comprising at least two further guidingedges of which a further first and a further second guiding edge arespaced apart from each other by a distance d of at least 0.5 mm, saidfurther first and said further second guiding edges being provided forsimultaneously contacting said dentist cutting tool thereby guiding saiddentist cutting tool in such a manner as to enable a guided removal ofat least partially said predetermined part of tooth structure; producingat least one further overlay (1) each having one of said at least onefurther guiding means (7).
 9. Method according to claim 8, characterisedin that said overlay and said at least one further overlay form a set ofoverlays to be used by a dentist in removing tooth structure for placinga crown or a bridge, said set of overlays comprising five overlays inwhich: a first overlay is determined so as to smoothen an upper part ofthe tooth thereby considering the desired height of the remaining toothstructure; a second overlay is determined so as to cut away one of thelongitudinal or transversal sides of the tooth; a third overlay isdetermined so as to cut away the other of the longitudinal ortransversal sides of the tooth; a fourth overlay is determined so as toround off edges between the longitudinal and transversal sides of thetooth at one side of the tooth; a fifth overlay is determined so as toround off edges between the longitudinal and transversal sides of thetooth at the other side of the tooth.
 10. Method according to claim 1,characterised in said overlays are produced via rapid prototyping. 11.Method according to claim 1 characterised in that said distance d is atleast 1 mm, preferably at least 2 mm, more preferably at least 3 mm,most preferably at least 4 mm.
 12. Overlay (1) to be used by a dentistin removing tooth structure from a tooth of a patient, which tooth is tobe prepared for further treatment, said overlay (1) being obtainable bythe method as claimed in claim
 1. 13. Set of overlays (1) to be used bya dentist in removing tooth structure from a tooth of a patient, whichtooth is to be prepared for further treatment, said set of overlays (1)being obtainable by the method as claimed in claim
 8. 14. Method forpreparing a tooth for further treatment using an overlay according toclaim 12.